Because the petroleum source is limited, various kinds of substitutive energy are developed extensively and turned into products. Among those, the solar cell has become the commercial products for either the industrial or the residential use, and the III-V group material solar cell is mainly applied to the space industry and the industrial field because of its high conversion efficiency.
However, there are many kinds of defects existing in/on the epitaxial layer of III-V group material. For example, as shown in FIG. 1, a pinhole defect 101 which is usually caused by a dislocation under stress occurs during the epitaxial growth of the III-V group material, and cracks 102 along the lattices also happen, especially in the wafer bonding process or the substrate transferring process. There are other kinds of defects, such as particles on the epitaxial layer or hilllocks which are particles covered by the epitaxial layer and exists in the epitaxial layer. These defects in/on the epitaxial layer result in device problems such as current leakage, and make the photovoltaic device operate abnormally. As the demand for a larger size photovoltaic device increases, the yield loss due to the defect becomes higher. For example, a 4-inch wafer produces only two photovoltaic devices used in aerospace industry, and the defect in/on the epitaxial layer results in 50% yield loss accordingly. In some prior art, a laser is used to burn and remove, the defects. However, it is difficult to remove the residual material produced in the laser treatment, and the residual material may also lead to a current leakage.